Dicamba is a selective herbicide currently used for treating e.g. corn, wheat or grassland. It kills broadleaf weeds before and after they sprout. The trivial name dicamba refers to the compound 3,6-dichloro-2-methoxybenzoic acid.
Dicamba is typically produced on an industrial scale from 2,5-dichlorophenol using carboxyla-tion under Kolbe-Schmitt conditions, methylation and subsequently saponification/acidification. 2,5-Dichorophenol in turn can be obtained from 1,4-dichlorobenzene or 1,2,4-trichlorobenzene. The synthetic route via 1,4-dichlorobenzene involves nitration and subsequent diazotation, and, therefore is undesired for use on an industrial scale. The synthetic route via 1,2,4-trichlorobenzene suffers from limited availability of this starting material and from the formation of several byproducts which are formed in the synthesis of 2,5-dichlorophenol.
In order to meet the increasing market demand for compounds such as dicamba, there is a need in the art for processes providing 2,5-dichlorophenol with acceptable purity and/or better overall purification efficiency, so that the limited resources of this compound can be used more efficiently.
The object of the present invention is to meet the above need. In particular, it is the object of the present invention to provide a process for purifying 2,5-dichlorophenol with improved overall purification efficiency and/or high purity. The process according to the present invention is cost effective and can be carried out on an industrial scale.